1. Field of the Invention
The present invention relates to animation and, more particularly, to a system and method of creating and animating a computer-generated image of a creature.
2. Description of the Related Art
An animation sequence is a series of frames that illustrate a scene that changes over time. In one animation technique, selected frames from a to-be-created sequence, known as key frames, are identified by a lead animator. The lead animator then describes every object in the key frames. The key frames are then passed on to a junior animator to fill in the frames that lie in between the key frames. As a result, the work performed by the junior animator is often referred to as “in-betweening.”
Computers are commonly used to assist in the animation process. One of the great promises of computer animation is that a lead animator can describe every object in the key frames, and the computer can then automatically perform the in-betweening. One of the problems with computer animation, in addition to a generally poor quality of in-betweening, is that it is generally quite difficult to create the key frames of the sequence.
For example, a humanoid creature is typically described with a hierarchical object model that includes a number of jointed polyhedral objects. The jointed objects of the creature can include, for example, the head, the neck, the chest, the stomach, the pelvis, the upper legs, the lower legs, the feet, the upper arms, the lower arms, and the hands.
The spatial relationship between two objects is described by translations, rotations, and other position-describing operators located at the joint between the two objects. Thus, to move one object (e.g., a leg) with respect to another object (e.g., a pelvis), the animator must change the translations, rotations, and other position-describing operators of the joint between the two objects.
For simple movements, such as to move the position of a forearm while keeping the position of the elbow fixed, modifying the position-describing operators is a straight-forward task. However, for more complex movements, modifying the position-describing operators can become an extremely difficult task.
One of the reasons for this is the hierarchical nature of the object model. With a hierarchical object model, the movement of one object can cause a number of other objects to move. For example, the hip or chest objects move all of the remaining objects. On the other hand, the arm object moves the hand related objects but not the leg objects.
Thus, to specify the position of a humanoid creature in a new key frame, the animator must decide if only the arms need to be moved, the arms and the chest, or the arms, the chest, and the stomach, and so on. If the animator specifies a new position of the chest object, then specifies a new position of the arm object only to find out that the animator should have begun with the stomach object, the entire process must be repeated.
Thus, there is a need for a system and method of animating a computer-generated image of a creature that reduces the difficulties associated with posing a to-be-animated creature in a new key frame.